To the original poster, it appears you weren't circumsized? If that is the case, and you haven't made it a habit to clean the meatus (the sensitive head portion when you pull back the foreskin), you could get what is called smegma.
Does it look flaky little pieces? If you try to smell it, does it smell pretty bad? If it is, then it's probably smegma. It's your penis' response to a dirty build up of bacteria, other substances with a natural soap. This accumulates into smegma, or what the guy above me says "dink cheese".
Just be sure to keep it clean, you don't want a girl smelling that if and when she may be down there. Major turn off.
P.S. if the reason why you have this build up is because you can't clean it because you can't pull back the foreskin to reveal the meatus, research phimosis.
Take care